Terrible things happen when you fire and fire your machine gun without switching barrels. The barrel becomes VERY HOT, which can cause:

a cookoff

a warped barrel

a worn-out bolt and barrel

ruined headspacing, which can cause the machine gun to explode .during firing

That's why the M2, M240, and M249 machine guns come with a spare barrel and why it's important you keep track of rounds fired and rate of fire. Take the spare to the field and change barrels when your machine gun needs it.

M2 Limits Changed

The rule on when you change the M2 machine gun's barrel has changed. The old rule was that you changed the M2 barrel at the end of a day of firing no matter how many rounds were fired. No more. If you're firing single shot, you can still wait until the end of the day to change barrels.

But if you're firing slow fire (40 or fewer rounds per minute), change the barrel every hour and if you're firing rapid fire (200 rounds per minute), change it every 1/2 hour.

Other Machine Gun Limits

For the M240, change the barrel every 10 minutes during sustained tire (100 rounds per minute) and every two minutes during rapid fire (200 rounds per minute).

For the M249, during both sustained fire (40 rounds per minute) and rapid fire (100 rounds per minute), change the barrel every 200 rounds.

Change the barrel even more frequently on hot days. Heat heats up the barrel quicker. And remember blanks heat up a barrel just as much as live rounds.